Method and apparatus for perforating formations in response to tubing pressure

Abstract

The present invention presents a method and apparatus for perforating a well in response to fluid pressure in a first tubing string while establishing a pressure balance in response to pressure in a second string, or in the well casing, through which the well will be produced. Additionally, redundant firing heads may be provided for perforating guns utilized to assure optimal reliability of the system. One or more perforating equipment assemblies may be employed in a tool string, each of which includes redundant firing mechanisms responsive to pressure in the tool string. Additionally, a firing head assembly is utilized which is initially responsive to pressure in the tool string, but which is subsequently actuated by annulus pressure. The firing head is suitable for use with much lower annulus pressures than are utilized with conventional hydraulically actuated firing head assemblies.

What is claimed is: 
     
       1. An apparatus for perforating a well, comprising: a packer;   a first tool string extending through said packer and including at least one perforating assembly, said perforating assembly comprising, a tubing string;   a first firing head assembly in fluid communication with said tubing string,   a second firing head assembly in fluid communication with said tubing string,   a perforating gun assembly including at least one perforating gun, said assembly operatively coupled proximate one end to said first firing head and operatively coupled proximate a second end to said second firing head; and     a second tool string providing a passageway for the flow of fluid from a location beneath said packer to the surface.   
     
     
       2. The apparatus of claim 1, wherein said packer is a dual packer and wherein said second tool string is operatively coupled to said packer. 
     
     
       3. An apparatus for perforating a well, comprising: a first tool string, comprising, a tubing string,   a dual packer in said tubing string,   a first branching block in said tubing string for establishing a string of equipment coextensive with a portion of said tubing string,   a first firing head assembly operatively coupled to said first branching block, said first firing head assembly responsive to fluid pressure in said tubing string,   a perforating gun operatively coupled proximate one end to said first firing head assembly,   a second firing head assembly operatively coupled proximate a second end of said perforating gun, said second firing head assembly responsive to fluid pressure in said tubing string,   a second branching block coupled in said tubing string, said second branching block also coupled to said second firing head assembly; and   a second tool string coupled to said dual packer to provide a fluid path from beneath said packer to the surface.     
     
     
       4. The apparatus of claim 3, wherein each of said first and second firing head assemblies are responsive initially to fluid pressure in said tubing string of said first tool string, and are subsequently responsive to fluid pressure outside said first tool string. 
     
     
       5. The apparatus of claim 4, wherein each of said first and second firing head assemblies comprises: an actuator mechanism responsive to fluid pressure in said first tool string; and   a detonation mechanism comprising, a securing assembly, said securing assembly releasable by said actuator mechanism, and   a piston mechanism responsive to fluid pressure in the well surrounding said firing head assembly.     
     
     
       6. A firing head for a perforating gun, comprising: a housing including first and second chambers and adapted to be positioned within a well, said first chamber in fluid communication with a tubing string and said second chamber in fluid communication with said well surrounding said firing head;   an actuator piston movably responsive to fluid pressure in said first chamber in said housing; and   a detonation assembly, comprising, a striking piston,   a locking assembly means for retaining said striking piston in a first position in said housing, said locking assembly releasable by movement of said actuating piston, and   means for causing movement of said striking piston from said first position to a second position in response to pressure in said second chamber of said housing after said locking assembly is released.     
     
     
       7. The firing head of claim 6, wherein said means for causing movement of said striking piston in response to pressure in said second chamber comprises a third chamber on one side of a portion of said striking piston, said third chamber at generally atmospheric pressure. 
     
     
       8. A method for perforating a well and a formation surrounding said well, comprising the steps of: establishing a first tool string in said well, said tool string comprising, a tubing string,   a first firing head responsive to fluid pressure in said tubing string,   a second firing head responsive to fluid pressure in said tubing string, and   a perforating gun operatively coupled proximate one end to said first firing head and operatively coupled proximate second end to said second firing head;     establishing a second tool string in said well;   establishing a pressure in said well adjacent said zone to be perforated through use of said second tubing string; and   causing said first and second firing heads to be actuated by establishing a fluid pressure in said first tool string.   
     
     
       9. The method of claim 8, wherein said first tool string further comprises a first packer located in said well above said formation to be perforated, and wherein said second tool string provides a flow path from beneath said first packer to the surface 
     
     
       10. The method of claim 9, wherein said first tool string further comprises: a second packer located beneath said first zone to be perforated;   a perforating gun coupled beneath said second packer;   a firing head operatively coupled to said perforating gun; and   a ported member to establish a flow path from beneath said second packer into said first tool string.   
     
     
       11. The method of claim 9, wherein said first tool string further comprises: a third firing head responsive to fluid pressure in said tubing string;   a fourth firing head responsive to fluid pressure in said tubing string; and   a second perforating gun operatively coupled proximate one end to said third firing head and operatively coupled proximate a second end to said fourth firing head.   
     
     
       12. An apparatus for perforating a well, comprising: a first packer;   a first tool string extending through said first packer, said first tool string comprising, at least one perforating assembly, said perforating assembly comprising,   a tubing string,   a first firing head assembly in fluid communication with said tubing string,   a second firing head assembly in fluid communication with said tubing string, and   a first a perforating gun assembly including at least one perforating gun, said first perforating gun assembly operatively coupled proximate one end to said first firing head and operatively coupled proximate a second end to said second firing head,   a second packer, said second packer located beneath said perforating assembly;   a second perforating gun assembly coupled beneath said second packer;   means operatively coupled to said second perforating gun assembly for activating said second perforating gun assembly; and   a ported member coupled in said first tool string to provide a flow path from beneath said second packer into said first tool string; and     a second tool string providing a passageway for the flow of fluid from a location below said first packer to the surface.   
     
     
       13. An apparatus for perforating a well, comprising: a packer;   a first tool string extending through said packer comprising, a first perforating assembly comprising,   a tubing string,   a first firing head assembly in fluid communication with said tubing string,   a second firing head assembly in fluid communication with said tubing string, and   a first perforating gun assembly including at least one perforating gun, said first perforating gun assembly operatively coupled proximate one end to said first firing head assembly and operatively coupled proximate a second end to said second firing head assembly;     a second perforating assembly comprising, a third firing head assembly in fluid communication with said tubing string,   a fourth firing head assembly in fluid communication with said tubing string; and   a second perforating gun assembly including at least one perforating gun, said second perforating gun assembly operatively coupled proximate one end to said third firing head assembly and operatively coupled proximate a second end to said fourth firing head assembly.